On Thursday, the Wall Street Journalpublished a troubling report that questions the accuracy and success of blood tests created by Theranos, a medical technology company helmed by Elizabeth Holmes, who founded the startup in 2003 as a 19-year-old student at Stanford University. According to the WSJ, the company’s technology–which Theranos says can run multiple medical tests using just a few drops of blood, as little as a finger prick–was only being used for 15 of the more than 240 variety of tests Theranos conducts.

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“At the end of 2014, the lab instrument developed as the linchpin of its strategy handled just a small fraction of the tests then sold to consumers,” the WSJ wrote, citing unnamed former employees of Theranos.

The anonymous former Theranos employees told the WSJ that they questioned the accuracy of the company’s device, and that many other tests offered by Theranos were carried out on standard equipment from mainstream manufacturers like Siemens.

In a blog post today, Theranos has vehemently denied the claims outlined by the WSJ, calling the article “factually and scientifically erroneous and grounded in baseless assertions by inexperienced and disgruntled former employees and industry incumbents.” Theranos says it gave the WSJ access to more than 1,000 pages of documents that allegedly refuted the information provided by the former employees, to whom the WSJ attributed many statements.

Theranos also said in the blog post that it sought FDA approval even though it wasn’t a requirement: Since Theranos only uses its technology in-house, it doesn’t need to be approved by the FDA. As the blog post notes, the WSJ story makes allegations against the exact technology that the FDA has signed off on.

The WSJ‘s report essentially argues that the device developed by Theranos, called Edison, may not be operating as advertised. It states that former employees were concerned about the accuracy of Edison results, particularly when directly compared against results from another machine. From the WSJ article:

In early 2014, Theranos split some of the proficiency-testing samples it got into two pieces, according to internal emails reviewed by the Journal. One was tested with Edison machines and the other with instruments from other companies.

The two types of equipment gave different results when testing for vitamin D, two thyroid hormones and prostate cancer. The gap suggested to some employees that the Edison results were off, according to the internal emails and people familiar with the findings.

The WSJ also spoke to doctors and nurses, who said Theranos results were sometimes inconsistent with those obtained through other machines. Throughout the article, all of these claims were systematically dismissed by the company’s general counsel and external lawyer.

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Valued at $9 billion, Theranos was started by Holmes when she was a 19-year-old sophomore at Stanford; Holmes dropped out of college soon after, to focus on the company full time. Investors have funneled hundreds of millions of dollars into the company, and Holmes, who is considered the first self-made female billionaire, has been compared to Steve Jobs on more than a few occasions.

Earlier this year, Fast Company lauded Theranos, touting it as one of 2015’s most innovative companies in the health care sphere for “introducing a better blood test”:

Instead of doctors sending vials of blood to a lab and waiting days to receive results, the Theranos test can be done at a pharmacy and requires only a painless finger prick for a tiny drop of blood, and results can be processed within four hours. In addition, Theranos is charging a fraction of the cost—$2 to $4 for basic blood tests, instead of what can cost thousands of dollars today. If all blood tests were performed at such low prices, it could save Medicare and Medicaid $202 billion over the next decade, according to the company’s estimates.

Fast Company has reached out to Theranos for comment. We will update this post if we hear back.